Copolymers of a perfluorochloroethylene and a fluoroethylene and method for their preparation



June 26, 1956 MOLE FRACTION M IN COPOLYMER A. L. DlTTMAN ETAL 2,752,331 COPOLYMERS OF A PERFLUOROCHLOROETHYLENE AND A FLUOROETHYLENE AND METHOD FOR THEIR PREPARATION Filed Jan. 21. 1953 I.O I

M1: CFZ: CFC! 11: 0.52

Mg: CFZ CH2 b2: O.l7

L0 o.e 0.6 0.4 0.2 0.0

MOLE FRACTION M1 IN FEED INVENTORS ALBERT DITTMAN HERBERT J. PASSINO WILBER O-TEETERS BY A TO NEYS United States Patent :COPOLYMERS OF A PERFLUOROCHLOROETHYL- ENE AND A FLUOROETHYLENE AND-METHOD FOR THEIR PREPARATION Albert L. 'Dittman, North Bergen, Herbert J. Passino, Englewood, and Wilber O. Teeters, RiverEdge, N. 1., assignors to The M. W. Kellogg Company,Jersey-City, N. J., a corporation of Delaware Application January 21, 1953, Serial No. 332,218 Claims. (Cl. 260-87.7)

This invention relates to halogen-containing polymeric materials. In one aspect, the invention relates to halogencontaining copolymers. More particularly in this aspect, the invention relates to copolymers of a perfluorochloroethylene and a fiuoroethylene and the method for their preparation.

This invention is a continuation-in-part of our prior and copending application Serial No. 213,298, filed February 28, 1951.

As an accumulative group, halogen-containing polymers offer wide utility in various industrial applications, servingnot only as substitutes for natural rubbers, but in some instances the various individual synthetics are superior to the natural products, e. g., in oil-resistance and aging characteristics. In this respect, polymers containing fluorine have been found to be both relatively inert and to possess good physical and chemical stability. One of the most useful polymers in this field is the perfluorochloroethylene polymer of trifluorochloroethylene. This particular polymer of trifluorochloroethylene has now been developed to a stage in which it is commercially available and has many useful applications by reason off its chemical inertness, and high physical strength and resilence, when in the form of a plastic. Four-fifths of the weight of polytrifluorochloroethylene is made up of fluorine and chlorine. The plastic form of polytrifluorochloroethylene is colorless and transparent, and has a high chemical stability with no effect being observed on the polymer after prolonged exposure to hydrofluoric acid, hydrochloric acid, and strong caustic solutions, as well as concentrated sulfuric acid, fuming nitric acid, aqua regia and other vigorous oxidizing materials. The plastic form of this polymer exhibits flexiblity and resilience, is not affected by water, or by humidity, and, in general, is an eflicient insulating material.

With particular reference to the utility of perfluorochloroethylene polymers, such as trifluorochloroethylene, it has been found desirable to employ these polymersas substitutes for natural rubbers, with the added physical and chemical advantages, as mentioned above, inherent 'in those polymers themselves. In this respect, the rubberlike polymers to be produced should display elastomeric properties, high tensile strength, flexibility at relatively low temperatures and should be easily vulcanized. While trifluorochloroethylene, however, as a perfluorochloroethylene polymer, possesses the above-mentioned physical and chemical properties, no synthetic rubber has been developed, prior to this invention, which possesses chemical inertness, high tensile strength, low temperature properties of flexibility, solubility in various solvents and vehicles, and which is also elastomeric and easily vulcanized.

It is, therefore, an object of this invention to provide new elastomeric copolymers having desirable physical and chemical characteristics, exhibiting the properties of corrosion-resistance to oils, fuels and various powerful reagents, and at the same time, possessing high tensile 2 strength, flexibility at relatively low temperatures, solubility in various solvents and vehicles, and which are elastomeric and easily vulcanized.

Another object ofthis invention is to provide a method for the manufacture of such copolymers having the'aforementioned characteristics.

Various other objects and advantages of the present invention will become apparent to those skilled in the art from the accompanying description and disclosure.

The polymers of the present invention are elastomeric copolmers of a perfluorochloroethylene, such as trifluorochloroethylene, and a fluoroethylene, such as vinylidene fluoride and are of a special value as durable fabriccoating compositions. The copolymers of the present invention contain between about mole per cent and about 69 mole per cent of the perfluorochloroethylene, and the remaining major constituent is a fluoroethylene. In general, as more fully hereinafter described, these copolymers are prepared by copolymerizing the perfluorochloroethylene (e. g., trifluorochloroethylene) with the fluoroethylene (e. g., vinylidene fluoride) at temperatures between about C. and about C. in the presence of a polymerization catalyst, either as an inorganic promoter in the form of a water-suspension type recipe or as an organic peroxide promoter in mass or bulk type polymerization. The copolymerization of the aforementioned monomers produces rubber-like elastomeric copolymers. These copolymers are flexible and elastic, even at temperatures as low as F., vulcanizable, chemically and thermally stable, oil and fuel resistant, soluble in various solvents and vehicles, and are particularly suited as durable, flexible coatings for application to fabric surfaces.

As indicated above, the polymers of the present inven tion are elastomeric copolymers of a perfluorochloroethylene, such as trifiuoroc'hloroethylene, (CF2=CFC1), and a fiuoroethylene, such as vinylidene fluoride,

In carrying out the polymerization reaction between the perfluorochloroethylene and the fluoroethylene monomers to produce the copolymers of the present invention, it has been indicated that the finished copolymers contain between about 20 mole per cent and 69 mole per cent of the perfluorochloroethylene, with the remaining major constituent being the fluoroethylene. If the finished copolymer contains less than about 20 mole per cent of the perfluorochloroethylene monomer, the copolymer exhibits a tendency to lose its desirable properties of corrosion-resistance to oils, fuels and other powerful reagents, due to the high increase influorochloroethylene content. If one the other hand, the finished copolymer cotains more than about 69 mole per cent of the perfluorochloroethylene monomer, the copolymer tends' to exhibit stiffness and reduced flexibility, and thusl'oses'it's desirable elastomeric properties. Within this critical range, it is preferred that the finished copolymers contain between about 25 mole per cent and about 50 mole per cent of the perfluorochloroethylene monomer, with the fluoroethylene monomer constituting the remaining major constituent.

To attain all the advantages inherent in each of the.

mentioned desired physical 'tend'to'be distorted.

The polymerization reaction is carried out, as indicated above, at a temperature between about 25 C. and about 50 C. When the polymerization promoter is in the form of a water-suspension type recipe, the reaction is preferably carried out at a temperature between about C. and about 35 C. When the polymerization promoter is an organic peroxide promoter in a mass polymerization system, the reaction is preferably carried out at a temperature between about 20 C. and about 0 C.

Of the water-suspension recipe type catalysts, a redox catalyst system is preferred (having no emulsifier), and

contains an oxidant, a reductant and a variable valence metal salt.

The oxidant in the water-suspension type recipe is preferably an inorganic persulfate such as potassium persulfate, sodium persulfate or ammonium persulfate, the former being most desirable. The reductant is preferablya bisulfite such as sodium bisulfite or potassium bisulfite, and preferably the former. The variable valence metal salt, which is employed for the purpose of regenerating the oxidant, is preferably in the form of an iron salt such as ferrous sulfate or ferrous nitrate with ferrous sulfate being the most desirable variable valence metal salt. Of the organic peroxide promoters halogen substituted acetyl peroxides are employed in carrying out the copolymerization in the absence of a suspension agent. Trichloroacetyl peroxide is a preferred promoter of this type. Other halogen substituted organic peroxides suitable for carrying out the copolymerization are trifluoro- 'acetyl peroxide, difluoroacetyl peroxide, 2,4-dichlorobenzoyl peroxide, chloroacetyl peroxide, trifluorodichloropropionyl peroxide, and dichlorofluoroacetyl peroxide.

In carrying out the abovc-mentioned polymerization procedure, the monomer reactivity ratios for the perfluorochloroethylene and the fluoroethylene, are calculated in accordance with the Mayo, Lewis and Walling equation.

This equation is represented as follows:

1 2] iHTzi d wherein r1 and r2 are parameters, M1 and M2 are concentrations in moles of monomer l and monomer 2. The equation describes the composition of the copolymer being formed at any instant,

diMi] dEMz] from a polymerization mixture of two monomers at concentrations M1 and M2 by means of two parameters, r1

and r2. These parameters (i. e., the monomer reactivity ratios), each represent the ratio of two rate constants for the reaction of a chain with a given monomer unit on the growing end with its own type of monomer, and

during polymerization, and results in a strong tendency towards alternation in this system. These values also in- .dicate that there is an azeotropic feed ratio at which the copolymer and monomer composition remain identical over the entire conversion scale.

An instantaneous copolymer feed-composition diagram,

derived from the above values, is shown in the accompanying drawing. By reference to the: curved line of the drawing, the proper'feed may be selected for the instan- Reference: "Copolymerization, F. R. Mayo and Cheves Walling, Chemical Reviews, v01. -16, pages 195197.

and chemical properties may taneous preparation of the copolymer, of desired composition, having between about 20 mole per cent and 69 mole per cent of trifluorochloroethylene, and the remaining major constituent being vinylidene fluoride.

According to this diagram, a /35 molar ratio of trifluorochloroethylene/vinylidene fluoride copolymer, is azeotropic, as shown by the straight line of the drawing, that is, the composition of the copolymer remains constant and equal to that of the feed over the entire range of up to approximately 100 per cent conversion. If an attempt is made to prepare a particular copolymer ratio (other than the azeotropic molar ratio), by feeding a single charge of constant composition (i. e., one which has been calculated to yield instantaneously a copolymer of desired composition), the less reactive monomer will lag in the reaction. As the copolymerization proceeds, the copolymer becomes excessively rich in the more re active monomer and assumes, to a greater degree, the properties characteristic of the more reactive monomer. As the relative concentration of the less reactive monomer to the more reactive monomer increases, the less reactive monomer is drawn more and more into the reaction. The copolymer produced becomes rich in respect to that monomer and eventually a homo polymer of the less reactive monomer will be obtained when the more reactive monomer is exhausted. This unevenness of reaction leads to an excessive spread in molar ratios found in the resulting copolymers.

In view of the inequality of reactivity, the charging of the monomers to the reactor, either in increments or as a continuous charge, should be carried out in such manner that the resulting copolymer composition varies by not more than 1-2 mole per cent from chain to chain.

It has been found that the perfluorochloroethylene/ fluoroethylene copolymers, e. g., copolymers of trifluorochloroethylene and vinylidene fluoride, which have an initial molar ratio of 50/50, vary to such an extent that at a conversion between about 70 and 80 per cent, the trifluorochloroethylene will be exhausted from the feed, and that any polymers produced thereafter will comprise pure polyvinylidenc fluoride. If the copolymer product is to be made sufliciently homogeneous, the monomers must be added incrementally or continuously so that the monomer composition is maintained at a constant level or the conversion is restricted to about 35 per cent, where the copolymer does not vary by more than :2 mole per cent from the average. To produce a copolymer of desired molar ratio through increment feeding, it is necessary to determine the molar ratio required for the initial monomer charge, which will, at the instant polymerization begins, yield a copolymer of desired molar ratio. As the concentration of the less reactive monomer increases, increment charges of composition designed to restore or maintain the molar ratio of the monomer phase at or near the initial molar level, are added. The number of increment feedings will be governed by the molar spread which may be tolerated. When the increment charges become so numerous as to be continuous, a charge of constant composition (the composition being equal to the molar ratio of the copolymer being formed) may be pumped into the polymerization reactor at a rate equal to the rate of polymerization. The variations involved in continuous feeding will be limited to the errors imposed by the pumping apparatus itself.

In general, the feed composition will comprise between about 5 mole per cent and about mole per cent of the perfluorochloroethylene and the remainder of the copolymer feed being made up of the fluoroethylene to produce a copolymer comprising between about 20 and about 69 mole per cent of the perfluorochloroethylene. To produce a copolymer within the preferred range in which the perfluorochloroethylene is present in an amount of between about 25 and about 50 mole per cent, the feed composition will comprise between about 7 mole per cent and about 40 mole per cent of the perfluorochloroethylene.

The aforementioned copolymerization reaction between the perfluorochloroethylene and the fiuoroetliylene monomers to produce the copolym ers of the present invention, is carried out at pressures between about 50 and about 525 pounds per square inch.

As previously indicated, the copolymers of the present invention are particularly suited and useful as durable, flexible coatings for application to fabric surfaces. Particularly useful solvents comprise the aliphatic and aromatic esters, the ether alcohols, and ketones. Typical examples of these solvents are di-isobutyl lietone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methoxy ethanol, ethoxy ethanol, ethyoxy ethoxy ethanol, methyl acetate, butyl acetate and ethyl benzoate. In this respect, it should be noted that it is often desirable to reduce the molecular weight of the finished copolymer of the present invention, in order to obtain greater solubility in organic solvents, such as those indicated above. This is of importance in order to obtain increased softness in the rubbery characteristics of the polymer for easier processability. The polymerization reactions which are carried out in the presence of the polymerization type catalysts of the present invention normally tend to form very high molecular weight copolymeric products. Reduction of the strength of the recipe or polymerization catalyst merely slows the rate of reaction without affecting, appreciably the molecular weight of the finished copolymer. It has been found, however, that the addition of various polymerization modifiers, appreciably reduces the molecular weight of the copolymer products, and increases their solubility and ease of processability without affecting, unduly, the overall yield. Suitable polymerization modifiers include chloroform (CHCls), Freon 113 (CFzClCFClz), carbon tetrachloride (CC14), trichloroacetyl chloride (CClsCOCl), dodecyl rnercaptan and bromotrichloromethane CBrCls. These modifiers are preferably added in amounts between about 1 to parts, by weight, per 100 parts of total perfiuorochloroethylene and fluoroethylene monomers charged to the polymerization reaction. Of these modifiers dodecyl mercaptan is preferred. This particular modifier appears to be much more powerful in function, than any of the others disclosed above and is, therefore, preferably employed in quantities ranging from 0.01 to 0.3 part per 100 parts of total monomer charged to the polymerization reaction.

The following examples are offered for a better understanding of the present invention and are not to be construed as limiting its scope.

EXAMPLE I This example .is intended to illustrate the preparation of a copolymer of trifluorochloroethylene and vinylidene fluoride.

The following water-suspension type recipe was employed in carrying out the polymerization reaction:

Parts by weight Water, distilled 200 CF2=CFCl 1 64.5 CF2=CH2 1 35.5 K2S2Oa 1.0 Na2S205 0.4 FeSO4.7H2O 0.1

1 50/50 molar.

The bomb was then closed and evacuated. Thereafter,

64.5 parts of CF2=CFCl and 35.5 .parts of CF2=CHz were flash-distilled into 'it. The bomb was then rocked at room temperature (between about C. and about 5 C.) over a period of 48 hours.

The residual monomer was then vented from the bomb and a mixture of water and chunks of rubbery polymer were discharged. These chunks were washed with hot water to remove residual salts, and were then dried in vacuo at room temperature.

The mole per cent of CF2=CFCL combined in the resulting copolymeric product, and the per cent conversion as dependent upon the polymerization time, is indicated, from the data obtained in the following table:

The procedure, illustrated by Example I, was repeated except that the following water-suspension type recipe so was employed in the preparation of the trifluorochloroethylene/vinylidene fluoride copolymer:

Parts by weight Water, distilled 200 CF2=CFCl 73 35 CF =CH2 ..a 27

K2S2O3 1.0 Na2S2O5 0.4 FeSO4.7H2O 0.1

/40 molar. 40

The results obtained following the aforementioned procedure, in employing the aforementioned recipe, are indicated as follows:

ggggg Percent Mole Percent No. Time Oonver- CFFOFCI Hours sion Combined As previously indicated, the water-suspension recipe type catalysts, employed in carrying out the polymerization reaction to produce the improved 'copolymers of the present invention contain an oxidant, in the form of a persulfate, or other peroxy compounds, of this type; a reductant, which is preferably a bisulfite, and a variable valence metal salt, which is preferably in the form of an iron salt. In this respect, it should be noted that the presence of the reductant and variable valence metal salt makes possible an increase in the quantity of free radicals which facilitates the ease of polymerization. However, it is also within the scope of this invention to carry out the polymerization reaction with the aforementioned water-suspension type recipe, in which the recipe contains only an oxidant (e. g., one of the aforementioned peroxy compounds) and eliminate the presence of either the reductant or variable valence metal salt, 'or both.

The following examples are intended to illustrate the preparation of a copolymer of trifluorochloroethylene and vinylidene fluoride, employing a water-suspension type recipe, containing only an oxidant, of the peroxy type, viz., potassium persulfate. The presence of a reductant or a variable valence metal salt, has been eliminated.

7 EXAMPLE III The procedure, illustrated by Example I, was repeated except that the following water-suspension type recipe was employed in the preparation of the trifiuorochloroethylene/vinylidene fluoride copolymer:

Parts by weight Water, distilled 100 CF2'CFC1 1 85 CF2=CH2 1 l5 K2S20s 0.05

1 75/25 molar.

Catalyst and activator solution was prepared by dissolving 0.05 part of KzSzOs in 100 parts of water. To a silver-lined steel bomb, the potassium persulfate solution was charged. The contents of the bomb were then frozen, and the bomb was closed and evacuated. 85 parts of CF2=CFCl and parts of CF2=CH2 were then flashdistilled into the bomb. The bomb was then rocked at room temperature (between about C. and 35 C.) for a period of 63 hours.

The residual monomer was then vented from the bomb and a mixture of water and chunks of rubbery polymer were discharged. These chunks were Washed with hot water to remove residual salts, and were then dried in va-cuo at room temperature.

The mole per cent of CF2=CFCl combined in the copolymer was found to be 69 per cent with a 29 per cent conversion.

EXAMPLE IV The procedure, illustrated by Example III, was repeated except that the following water-suspension type recipe was employed in the preparation of the trifiuorochloroethylene/vinylidene fluoride copolymer:

1 25/75 molar.

Catalyst and activator solution was prepared by dissolving 0.5 part of K2S2Oa in 100 parts of water. To a silver-lined steel bomb the potassium persulfate solution was charged. The contents of the bomb were then frozen and the bomb was closed and exacuated. 38 parts of CF2=CFC1 and 62 parts of CF2=CH2 were then flashdistilled into the bomb. The bomb was then rocked at room temperature (between about 25 C. and about 35 C.) for a period of 21 hours.

The residual monomer was then vented from the bomb and a mixture of water and chunks of rubbery polymer were discharged. These chunks were washed with hot water to remove residual salts, and were then dried in va-cuo at room temperature.

The mole per cent of CF2=CFCl combined in the copolymer was found to be 25 per cent with a 70 per cent conversion.

EXAMPLE V This example is intended to illustrate the preparation of a copolymer of trifluorochloroethylene and vinylidene fluoride, employing an organic peroxide promoter, viz., trichloroacetyl peroxide, in a mass polymerization system.

The polymerization was carried out in a glass tubecontaining a feed comprising about 30 mole per cent trifluorochloroethylene and about 70 mole per cent vinylidene fluoride, in the presence of trichloroacetyl peroxide as the promoter. The tube was placed in a bath maintained at a temperature of approximately l:5 C. for a period of about seven days. At the end of that time, the tube was removed from the bath. The mole per cent of trifluorochloroethylene combined in the copolymer was found to be about 43.5 per cent with a 94.8 per cent conversion of the total monomers charged.

The finished copolymer was then pressed between chrome-plated ferrotype plates in an electrically heating carver press at a temperature of about 250 C., for a period of about five minutes. It was found that a clear, tough, flexible rubbery polymer sheet had been produced.

EXAMPLE VI The procedure, illustrated by Example V, was repeated, employing trichloroacetyl peroxide as an organic peroxide promoter, in a mass polymerization system.

The polymerization was carried out in a glass tube containing a feed comprising about 70 mole per cent trifiuorochloroethylene and about 30 mole per cent vinylidene fluoride. The tube was placed in a bath maintained at a temperature of approximately 15 C. for a period of about seven days. At the end of that time, the tube was removed from the bath. The mole per cent of trifluorochloroethylene combined in the copolymer was found to be about 65.6 per cent with a 74.4 per cent conversion of the total monomers charged.

The finished copolymer was then pressed between chrome-plated ferrotype plates in an electrically heating carver press at a temperature of about 250 C., for a period of about five minutes. It was found that a clear, tough, flexible rubbery polymer sheet had been produced.

As previously indicated, the copolymers of the present invention prepared by copolymerizing a perfluorochloroethylene with a fluoroethylene within the critical molar ratios and under the polymerization conditions previously described, possess unusual and highly desirable chemical and physical properties which make them particularly suited as durable, flexible coatings for application to various fabric surfaces. These surfaces may, in a preferred form for application, take the form of protective clothing (e. g., as suits, boots, gloves, helmets and other wearing apparel), and other articles of manufacture which are comprised of exposed surfaces which may be subjected to bending, folding, or other forms of distortion in the course of performing their function under special environmental conditions. Particular applicability of the copolymers of the present invention is to be found when they are employed as protective coatings on surfaces, such as stated above, which are to be subjected to environmental conditions in which they may come into contact with corrosive substances, such as, oils, fuels and various powerful reagents, as previously described, and over a wide temperature range. These copolymeric coatings are found to have high tensile strength, good elastomeric properties, hardness, high heat-resistance, and ease of solubility in various solvents, when in their raw copolymeric state for application to various surfaces and can be pressed into sheets at temperatures between about 350 F. and about 500 F. These advantages are only obtainable by forming the copolymers, under the polymerization conditions previously described, and within the molar ratios previously defined (viz., with a content of between about 20 mole per cent and about 69 mole per cent of the perfluorochloroethylene and the remaining major constituent being the fiuoroethylene).

When employed as protective coatings, for any of the surfaces described above, the raw copolymer is dissolved in a suitable solvent, such as those described above, to obtain an adherent cement. Particularly useful solvents for this purpose may comprise aliphatic and aromatic esters, ether alcohols and ketones. The raw polymer, which may also include fillers if so desired, is dissolved in the solvent, preferably to an extent in which the total quantity of solids represents 50 per cent by weight of the entire cement composition. The cement is now applied to the fabric, employing such apparatus as a knife-spreader, or doctor-blade, or a reverse roll-coater. The solvent,

.after thecement has been applied to the desired surfaces,

'vated temperature).

is permitted to evaporate from the surface of the fabric (and may also be accomplished in the presence of ele- After the solvent has completely evaporated, the coated surface is now ready for use. It should also be noted, that the cement, containing the aforementioned copolymer, may be applied to the surface either as a single coat, or if so desired, the protective coating may be built-up by the application of several layers of the cement, each layer being permitted to harden by solvent evaporation, before the next cement layer is applied. Furthermore, if so desired, the protective coating can be suitably pigmented, by adding various pigmenting agents to the cement mixture prior to application to the desired surface. It is also possible to apply the protective coating, in the form of a cement, by such methods as spraying, dipping, or brushing, if so desired.

The following table represents the characteristics obtained for a typical copolymer of the present invention, in which various critical properties are listed for a copolymer of trifluorochloroethylene and vinylidene fluoride, in a 50/50 molar ratio:

Properties of CF2=CFCUCF2=CH2 (50/50 molar) 5% nitric acid. Susceptibility to attack by microorganisms None. Effect of prolonged sunlight None. Effect of prolonged beta radiation None.

The most probable theory for the superiority of the copolymers of the present invention, containing between about 20 mole per cent and about 69 mole per cent of the perfluorochloroethylene (e. g., trifluorochloroethylene) and the remaining major constituent being the fluoroethylene (e. g., vinylidene fluoride) is the significance of the presence of at least one chlorine atom in the perfluorochloroethylene, attached to one or more carbon atoms, and at least one hydrogen atom in the fluoroethylene, attached to one or more of the carbon atoms. The chlorine atom in the perfluorochloroethylene is of importance in permitting copolymerization to take place easily between the perfluorochloroethylene and the fluoroethylene monomers. The hydrogen atom in the fluoroethylene is of importance in obtaining the aforementioned desirable characteristics of the copolymer. The fluorine atom attached to at least one of the carbon atoms in each of the perfluorochloroethylene and fluoroethylene monomers, is of importance in obtaining stability of the finished copolymer without atfecting the stability of the respective comonomers, during the polymerization reaction.

Since certain changes may be made in carrying out the process of the present invention in producing the desired copolymers, without departing from the scope of the invention, it is intended that all matter contained in the above description is to be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, we claim:

1. A copolymer of about 25 to about 50 mole per cent trifluorochloroethylene and correspondingly about 75 to about 50 mole per cent vinylidene fluoride as substantially the sole monomeric components.

2. An elastomeric copolymer of about 50 mole per cent trifluorochloroethylene and about 50 mole per cent vinylidene fluoride as substantially the sole monomeric components.

3. A method for preparing .a copolymer of about 25 to about 50 mole per cent trifluorochloroethylene and correspondingly about 75 -to about "50 mole. per cent vinylidene fluoride as substantially the sole monomeric components which comprises polymerizing a reaction mixture containing vinylidene fluoride and between about 7 mole per cent and about 40 mole per cent trifluorochloroethylene as substantially the sole monomeric components at a temperature between about -25 C. and about 50 C. in the presence of a polymerization promoter.

4. A method for preparing a copolymer of about 25 to about 50 mole per cent trifluorochloroethylene and correspondingly about 75 to about 50 mole per cent vinylidene fluoride as substantially the sole monomeric components which comprises polymerizing a reaction mixture containing vinylidene fluoride and between about 7 mole per cent and about 40 mole per cent trifluorochloroethylene as substantially the sole monomeric components at a temperature between about 0 C. and about 35 C. in the presence of a polymerization promoter.

5. A method for preparing a copolymer of about 25 to about 50 mole per cent trifluorochloroethylene and correspondingly about 75 to about 50 mole per cent vinylidene fluoride as substantially the sole monomeric components which comprises polymerizing a reaction mixture containing vinylidene fluoride and between about 7 mole per cent and about 40 mole per cent trifluorochloroethylene as substantially the sole monomeric components at a temperature between about -20 C. and about 0 C. in the presence of a polymerization promoter.

6. A method for preparing an elastomeric copolymer of about 25 to about 50 mole per cent trifluorochloroethylene and correspondingly about 75 to about 50 mole per cent vinylidene fluoride as substantially the sole monomeric components which comprises polymerizing a reaction mixture containing vinylidene fluoride and between about 7 mole per cent and about 40 mole per cent trifluorochloroethylene as substantially the sole monomeric components at a temperature between about 0 C. and about 35 C. in the presence of a polymerization promoter comprising a peroxy compound.

7. A method for preparing a copolymer of about 25 to about 50 mole per cent trifluorochloroethylene and correspondingly about 75 to about 50 mole per cent vinylidene fluoride as substantially the sole monomeric components which comprises polymerizing a reaction mixture containing vinylidene fluoride and between about 7 mole per cent and about 40 mole per cent trifluorochloroethylene as substantially the sole monomeric components at a temperature between about -25 C. and about 50 C. in the presence of a polymerization promoter comprising an organic peroxide compound.

8. A method for preparing a copolymer of about 25 to about 50 mole per cent trifluorochloroethylene and correspondingly about 75 to about 50 mole per cent vinylidene fluoride as substantially the sole monomeric components which comprises polymerizing a reaction mixture containing vinylidene fluoride and between about 7 mole per cent and about 40 mole per cent trifluorochloroethylene as substantially the sole monomeric components at a temperature between about 20 C. and about 0 C. in the presence of a polymerization promoter comprising a halogen-substituted acetyl peroxide.

9. An article of manufacture which comprises a fabric surface coated with a copolymer of about 25 to about 50 mole per cent trifluorochloroethylene and correspondingly about 75 to about 50 mole per cent vinylidene fluoride as substantially the sole monomeric components.

10. An article of manufacture which comprises a fabric surface covered with an elastomeric copolymer of about 50 mole per cent trifluorochloroethylene and about 50 T1 12 mole per cent vinylidene fluoride as silbstantially the sole 2,584,126 Hapford Q Feb 5, 1952 monomeric components. 2,599,640 Joyce June 10, 1952 2,631,998 Pearson Mar. 17, 1953 References Cited in the file of this patent 2,689,241 Dittman Sept. 14, 1954 UNITED STATES PATENTS 5 FOREIGN A S 2,456,255 Cofiman 14, 1948 590,390 Great Britain July 16, 1947 2,513,312 Hanford July 4, 1950 2,569,524 Hamilton Oct. 2, 1951 

1. A COPOLYMER OF ABOUT 25 TO ABOUT 50 MOLE PER CENT TRIFLUOROCHLOROETHYLENE AND CORRESPONDINGLY ABOUT 75 TO ABOUT 50 MOLE PER CENT VINYLIDENE FLUORIDE AS SUBSTANTIALLY THE SOLE MONOMERIC COMPONENTS. 